redis-py `hset` and `hmset` unexpectedly mutates the list

The Fix

pip install redis==7.1.0

Based on closed redis/redis-py issue #3052 · PR/commit linked

Jump to Verify Open PR/Commit

@@ -5017,14 +5017,16 @@ def hset(
         if key is None and not mapping and not items:
             raise DataError("'hset' with no key value pairs")
-        items = items or []
+        pieces = []
+        if items:

repro.py

from redis.client import Redis

redis = Redis.from_url('redis://127.0.0.1')

items = [
    'one', b'1',
    'two', b'2',
    'three', b'3',
]

redis.hset('test', items=items, key='four', value=b'4')

print(items)

redis.close()

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\npip install redis==7.1.0\nWhen NOT to use: Do not use this fix if the mutation of input lists is intended behavior.\n\n

Why This Fix Works in Production

Trigger: Calling the method should, in principle, not change any of the objects sent as parameters.
Mechanism: The `hset` method mutates the list passed to the `items` parameter when used with other parameters
Why the fix works: `HSET` unexpectedly mutates the list passed to `items` was fixed by changing how parameters are handled. (first fixed release: 7.1.0).

Production impact:

If left unfixed, this can cause silent data inconsistencies that propagate (bad cache entries, incorrect downstream decisions).

Why This Breaks in Prod

The `hset` method mutates the list passed to the `items` parameter when used with other parameters
Production symptom (often without a traceback): Calling the method should, in principle, not change any of the objects sent as parameters.

Proof / Evidence

GitHub issue: #3052
Fix PR: https://github.com/redis/redis-py/pull/3103
First fixed release: 7.1.0
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.95
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.65

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“**Version**: redis-py 5.0.1 (Any Redis version) **Platform**: Any platform **Description**: If the items parameter of the hset or hmset method is used in conjunction with the key and value, or with the mapping parameters, the list passed to”

Issue thread · issue description · source

Failure Signature (Search String)

Calling the method should, in principle, not change any of the objects sent as parameters.
As a suggestion, the code could be changed to:

Copy-friendly signature

signature.txt

Failure Signature
-----------------
Calling the method should, in principle, not change any of the objects sent as parameters.
As a suggestion, the code could be changed to:

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
Calling the method should, in principle, not change any of the objects sent as parameters.
As a suggestion, the code could be changed to:

Minimal Reproduction

repro.py

from redis.client import Redis

redis = Redis.from_url('redis://127.0.0.1')

items = [
    'one', b'1',
    'two', b'2',
    'three', b'3',
]

redis.hset('test', items=items, key='four', value=b'4')

print(items)

redis.close()

What Broke

Unexpected mutation of input lists leads to incorrect data being processed.

Why It Broke

The `hset` method mutates the list passed to the `items` parameter when used with other parameters

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

pip install redis==7.1.0

When NOT to use: Do not use this fix if the mutation of input lists is intended behavior.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/redis/redis-py/pull/3103

First fixed release: 7.1.0

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

Do not use this fix if the mutation of input lists is intended behavior.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Capture the exact failing error string in logs and tests so you can reproduce via a minimal script.
Pin production dependencies and upgrade only with a reproducible test that hits the failing path.

Version Compatibility Table

Version	Status
7.1.0	Fixed

Related Issues

No related fixes found.

Cluster: redis-py:data-consistency redis-py hub redis-py best practices All hubs All clusters

Related clusters: Configuration error Retry storm Race condition

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

redis-py `hset` and `hmset` unexpectedly mutates the list passed to `items` if `key`+`value` or (Fix)